Degenerate epitaxy-driven defects in monolayer silicon oxide onto ruthenium

The structure of the ultimately-thin crystalline allotrope of silicon oxide, prepared onto a ruthenium surface, is unveiled down to atomic scale with chemical sensitivity, thanks to high resolution scanning tunneling microscopy and first principle calculations. An ordered oxygen lattice is imaged which coexists with the two-dimensional monolayer oxide. This coexistence signals a displacive transformation from an oxygen reconstructed-Ru(0001) to silicon oxide, along which latterally-shifted domains form, each with equivalent and degenerate epitaxial relationships with the substrate. The unavoidable character of defects at boundaries between these domains appeals for the development of alternative methods capable of producing single-crystalline two-dimensional oxides

Insertion sequence content reflects genome plasticity in strains of the root nodule actinobacterium Frankia

<p>Abstract</p> <p>Background</p> <p>Genome analysis of three <it>Frankia sp. </it>strains has revealed a high number of transposable elements in two of the strains. Twelve out of the 20 major families of bacterial Insertion Sequence (IS) elements are represented in the 148 annotated transposases of <it>Frankia </it>strain HFPCcI3 (CcI3) comprising 3% of its total coding sequences (CDS). EAN1pec (EAN) has 183 transposase ORFs from 13 IS families comprising 2.2% of its CDS. Strain ACN14a (ACN) differs significantly from the other strains with only 33 transposase ORFs (0.5% of the total CDS) from 9 IS families.</p> <p>Results</p> <p>Insertion sequences in the <it>Frankia </it>genomes were analyzed using BLAST searches, PHYML phylogenies and the IRF (Inverted Repeat Finder) algorithms. To identify putative or decaying IS elements, a PSI-TBLASTN search was performed on all three genomes, identifying 36%, 39% and 12% additional putative transposase ORFs than originally annotated in strains CcI3, EAN and ACN, respectively. The distribution of transposase ORFs in each strain was then analysed using a sliding window, revealing significant clustering of elements in regions of the EAN and CcI3 genomes. Lastly the three genomes were aligned with the MAUVE multiple genome alignment tool, revealing several Large Chromosome Rearrangement (LCR) events; many of which correlate to transposase clusters.</p> <p>Conclusion</p> <p>Analysis of transposase ORFs in <it>Frankia </it>sp. revealed low inter-strain diversity of transposases, suggesting that the majority of transposase proliferation occurred without recent horizontal transfer of novel mobile elements from outside the genus. Exceptions to this include representatives from the IS3 family in strain EAN and seven IS4 transposases in all three strains that have a lower G+C content, suggesting recent horizontal transfer. The clustering of transposase ORFs near LCRs revealed a tendency for IS elements to be associated with regions of chromosome instability in the three strains. The results of this study suggest that IS elements may help drive chromosome differences in different <it>Frankia </it>sp. strains as they have adapted to a variety of hosts and environments.</p

6 mW and 30 mW laser threshold for respectively 1st and 2nd Brillouin Stokes order in a Ge10As24Se68 chalcogenide fiber

International audienceA compact second-order Stokes Brillouin fiber laser made of microstructured chalcogenide glass is reported for the first time. This laser has very low optical pump-power threshold for Stokes conversion: 6 mW for first order and only 30 mW for second order with nonresonant pumping

Towards More Coherent Sources Using a Microstructured Chalcogenide Brillouin Fiber Laser

International audienceUp to 16 dB frequency noise reduction and a linewidth 8 times narrower that of the pump source is reported for the Stokes component in a compact Brillouin fiber laser made of chalcogenide microstructured fiber. Since the pump wave is not resonant in the ring cavity, an active stabilization of the laser is not primordial thus making the system simpler and cheaper. Although only a 3 metre-long microstructured chalcogenide fiber was used as gain medium, a very low laser threshold power of 6 mW was obtained for nonresonant pumping. The linewidth-narrowing effect achieved in our BFL cavity is also discussed

Lasers Brillouin à fibre microstructurée en verre de chalcogénure à très faibles seuils

National audienceL'utilisation de fibres microstructurées en verre de chalcogénure ouvre la voie à la réalisation des lasers à fibre Brillouin présentant des seuils très bas comparativement aux lasers en fibre silice, de l'ordre du milliWatt en pompage non-résonant. Ces lasers sont compacts et par nature mono-fréquence. Leurs caractéristiques de bruit sont améliorées par rapport à la pompe comme cela a été déjà prédit pour les lasers Brillouin

Relative intensity noise and frequency noise of a compact Brillouin laser made of As38Se62 suspended-core chalcogenide fiber

International audienceRelative intensity noise and frequency noise have been measured for the first time for a single-frequency Brillouin chalcogenide As38Se62 fiber laser. This is also the first demonstration of a compact suspended-core fiber Brillouin laser, which exhibits a low threshold power of 22 mW and a slope efficiency of 26% for nonresonant pumping

Linewidth-narrowing and intensity noise reduction of the 2nd order Stokes component of a low threshold Brillouin laser made of Ge10As24Se68 chalcogenide fiber

International audienceA compact second-order Stokes Brillouin fiber laser made of microstructured chalcogenide fiber is reported for the first time. This laser required very low pump power for Stokes conversion: 6 mW for first order lasing and only 30 mW for second order lasing with nonresonant pumping. We also show linewidth-narrowing as well as intensity noise reduction for both the 1st and 2nd order Stokes component when compared to that of the pump source

Brillouin fiber laser using As38Se62 suspended-core chalcogenide fiber

International audienceIn this paper, an all-fiber Brillouin laser ring cavity using a 3-m-long suspended-core chalcogenide As38Se62 fiber is reported for the first time to our knowledge. For a nonresonant ring cavity with no servo-locking, a laser threshold power of 37 mW and an efficiency of 26 % were obtained for a fiber having a core diameter of 5 μm. The linewidth of the Brillouin fiber laser and the pump laser were respectively measured to be below 4 kHz, the resolution of our autocorrelator, and 250 kHz, thus showing the linewidth-narrowing nature of the Brillouin laser. This result paves the way to compact Brillouin lasers with low threshold power and good spectral purity. A full experimental Brillouin characterization is also reported. We measured a Brillouin gain spectrum of 14.2 MHz, a Brillouin gain coefficient of 5.6x10-9 m/W and a Brillouin frequency shift of 7.95 GHz in our fiber